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Saturday, October 1, 2011

Does brain plasticity trump innateness?

The fact that the adult brain is very plastic is often held up as evidence against the idea that many psychological, cognitive or behavioural traits are innately determined. At first glance, there does indeed appear to be a paradox. On the one hand, behavioural genetic studies show that many human psychological traits are strongly heritable and thus likely determined, at least in part, by innate biological differences. On the other, it is very clear that even the adult brain is highly plastic and changes itself in response to experience.

The evidence on both sides is very strong. In general, for traits like intelligence and personality characteristics such as extraversion, neuroticism or conscientiousness, among many others, the findings from genetic studies are remarkably consistent. Just as for physical traits, people who are more closely related resemble each other for psychological traits more than people with a more distant relationship. Twin study designs get around the obvious objection that such similarities might be due to having been raised together. Identical twins tend to be far more like each other for these traits than fraternal twins, though the family environment is shared in both cases. Even more telling, identical twins who are raised apart tend to be pretty much as similar to each other as pairs who are raised together. Clearly, we come fairly strongly pre-wired and the family environment has little effect on these kinds of traits.

Yet we know the brain can “change itself”. You could say that is one of its main jobs in fact – altering itself in response to experience to better adapt to the conditions in which it finds itself. For example, as children learn a language, their auditory system specialises to recognise the typical sounds of that language. Their brains become highly expert at distinguishing those sounds and, in the process, lose the ability to distinguish sounds they hear less often. (This is why many Japanese people cannot distinguish between the sounds of the letters “l” and “r”, for example, and why many Westerners have difficulty hearing the crucial tonal variations in languages like Cantonese). Learning motor skills similarly improves performance and induces structural changes in the relevant brain circuits. In fact, most circuits in the brain develop in an experience-dependent fashion, summed up by two adages: “cells that fire together, wire together” and “use it or lose it”.

Given the clear evidence for brain plasticity, the implication would seem to be that even if our brains come pre-wired with some particular tendencies, that experience, especially early experience, should be able to override them.

I would argue that the effect of experience-dependent development is typically exactly the opposite – that while the right kind of experience can, in principle, act to overcome innate tendencies, in practice, the effect is reversed. The reason is that our innate tendencies shape the experiences we have, leading us to select ones that tend instead to reinforce or even amplify these tendencies. Our environment does not just shape us – we shape it.

A child who is naturally shy – due to innate differences in the brain circuits mediating social behaviour, general anxiety, risk-aversion and other parameters – will tend to have less varied and less intense social experience. As a result, they will not develop the social skills that might make social interaction more enjoyable for them. A vicious circle emerges – perhaps intense practice in social situations would alter the preconfigured settings of a shy child’s social brain circuits but they tend not to get that experience, precisely because of those settings. In contrast, their extroverted classmates may, by constantly seeking out social interactions, continue to develop this innate faculty.

This circle may be most vicious in children with autism, most of whom have a reduced level of innate interest in other people. They tend, for example, not to find faces as intrinsically fascinating as other infants. This may contribute to a delay in language acquisition, as they miss out on interpersonal cues that strongly facilitate learning to speak.

A similar situation may hold for children who have difficulties in reading or with mathematics. Dyslexia seems to be caused by an innate difficulty in associating the sounds and shapes of letters. This can be traced to genetic effects during early development of the brain, which may cause interruptions in long-range connections between brain areas. This innate disadvantage is cruelly amplified by the typical experience of many dyslexics. Learning to read is hard enough and requires years of practice and active instruction. For children who have basic difficulties in recognising letters and words, reading remains effortful for far longer and they will therefore tend to read less, missing out on the intensive practice that would help their brain circuitry specialise for reading.

Though less widely known, dyscalculia (a selective difficulty in mathematics) is equally common and shares many characteristics with dyslexia. The initial problem is in innate number sense – the ability to estimate and compare small numbers of objects. This faculty is present in very young infants and even shared with many other animal species, notably crows. Formal mathematical instruction is required to build on this innate number sense but also crucially relies on it. As with reading, mathematics requires hard work to learn and if numbers are inherently mysterious then this will change the nature of the child’s experience, lessen interest and reduce practice. At the other end of the spectrum, those with strong mathematical talent may gravitate towards the subject, further amplifying the differences between these two groups.

Thus, while a certain type of experience can alter the innate tendency, the innate tendency makes getting that experience far less likely. Brain plasticity tends instead to amplify initial differences.

That sounds rather fatalistic, but the good news is that this vicious circle can be broken if innate difficulties are recognised early enough – by actively changing the nature of early experience. There is good evidence that intense early intervention in children with autism (such as Applied Behaviour Analysis) allows them to compensate for innate deficits and lead to improvements in cognitive, communication and adaptive skills. Similarly intense intervention in children with dyslexia has also proven effective. Thus, even if it is not possible to reverse whatever neurodevelopmental differences lead to these kinds of deficits, it should at least be possible to prevent their being amplified by subsequent experience.

Duff FJ, & Clarke PJ (2011). Practitioner Review: Reading disorders: what are the effective interventions and how should they be implemented and evaluated? Journal of child psychology and psychiatry, and allied disciplines, 52 (1), 3-12 PMID: 21039483

10 comments:

"This circle may be most vicious in children with autism, most of whom have a reduced level of innate interest in other people. They tend, for example, not to find faces as intrinsically fascinating as other infants."Evidence? References?

"There is good evidence that intense early intervention in children with autism (such as Applied Behaviour Analysis) allows them to compensate for innate deficits and lead to improvements in cognitive, communication and adaptive skills."The autism researcher Michelle Dawson seems to be often claiming the opposite. She recently mentioned "the problem of autism behavior analysts not declaring COIs in published papers, much less in "best practice" reports." In my experience, when researchers fail to declare conflicts of interest, that is a bad sign.

Thanks Lili for your comments. I know there are questions about the effectiveness of ABA and other behavioural treatments or early intensive educational interventions in autism. The view from the report you cite is: "Evidence suggests that there is an undefined subgroup of children for whom early and intensive behavioral interventions may elicit robust gains while others may not demonstrate marked improvement." As I said above, this is unlikely to reverse initial defects but may limit the amplification of these defects due to the interplay between innate preferences and experience.

There is lots of evidence that people with autism show less interest - as a group, on average - in faces. Here are a couple of recent studies: http://www.ncbi.nlm.nih.gov/pubmed/18787936http://www.ncbi.nlm.nih.gov/pubmed/21705475

There are many others. I should point out that this does not necessarily apply to all patients with a diagnosis of autism.

I couldn't find any details about the number and age of the subjects in one of those studies, so I can't tell if it supports your assertion about autistic infants.

The other study was small study involving adults, in which it was found that autistic were less distracted by "irrelevant face stimuli", which is surely a good thing. This study doesn't support your claim about autistic infants.

the adult brain work in a different way, with the years the brain develops a several functions, many of then work in a simple way, others for the contrary are so complicated, some experts from bmpharmacy research center are agreed in brain studies must be based more in functions that structure.

Just wanted to thank you, not just because the nice post, but pretty much more because my grandfather is nearly recovering from his surgery and he has almost nothing to do but staying on bed all day, his best source of entertainment has been this blog and xl pharmacy, I feel this is something good for him and his recovery.

Interesting post Kevin, thank you. Like Lili I'd like to comment on the example of 'children with autism'.

By definition, children and adults diagnosed with autism spectrum disorders have less well-developed social skills than most people. And clearly, "innate differences in the brain circuits mediating social behaviour, general anxiety, risk-aversion and other parameters…" would quite likely reduce their opportunities for rehearsing social skills and thus overcome those innate differences. But I think there are some pretty big assumptions being made here.

1. You've used the word 'innate' several times, but haven't actually defined it. Do you mean literally 'inborn', or 'with biological origins', or 'genetically determined'?

2. With that point in mind, the social behaviour, anxiety and risk-aversion of neonates aren't noted for their sophistication, so could you say what sort of differences you mean when you refer to 'innate differences in the brain circuits mediating social behaviour, general anxiety, risk-aversion and other parameters' and the 'preconfigured settings of a shy child’s social brain circuits'?

3. You cite studies showing that people with autism are less interested than controls in faces , but those studies don't show that that reduced interest is 'innate'. Even if there were evidence that newborns who later developed autistic characteristics were less interested in faces than infants who developed more typically, one would need to demonstrate that it was faces that were of less interest rather than faces as subsets of arrays with stable visuo-spatial features . There's been an ongoing interest in the visual processing issues involved in ASDs, after all. In other words, although we can say with some confidence that reduced interest in faces or social interaction are emergent properties of development that contribute to the characteristics of something we call 'autism', I'm not sure that we have any evidence that 'seeking out social interactions' (or not) is an 'innate faculty'.

I'm equally perplexed by the fact that you've equated dyscalculia with inability to subitize. Is there any evidence for this?

I appreciate your logic. It needs to be used more often, especially in regard to the autisms. It just seems anyone's guess is used as the basis for science, but it's like..."let's throw this at it and see if it sticks." Pub Med offers study after study that pretty much proves that. Proving it, is often inconsequential in my eyes, because you can always find both sides of a hypothesis represented, somehow.

But logic is logic.

ABA is as bad or as good as the practitioners who use it. (Lovaas had problems.) Seeing all children as children first is helpful. It is recognition of behavior brought down to what is perceived as it's most basic tenets. (I believe there are 4 functions of behavior, social attention, achieving desired tangible or activities, escape or avoidance, and to obtain pleasure.) Adults in positions of power can "educe" or draw forth that which is within. Because it makes children so vulnerable, testing for practitioners is very strict regarding ethics, 80% of those who fail the testing to become a Board Certified Behavior Analyst do so because of the ethics portion. But a great share of the people who work with the kids are off the street...and that is where the good or bad remains to be revealed. Behaviorism, in itself, makes the caregiver more predictable, and that is it's strength. To me, it seems like the more seriously autistic kids live in a mightily unpredictable world, through no fault of their own. It is a construct that can be used, and I worked at a residential school where 90% of the teachers were very calm and predictable. They got a lot of cooperation from kids who were placed there as wards of the state, their problems so severe their local school systems, and more sadly, their parents, could not handle them. For my mildly semantic-pragmatically disordered son, no...it was too intense. But for those kids, it made life livable.The teachers actually felt dispirited if they used punishment. Like a parent, it feels like failure on your part if you have to punish your child.

Anyhow, it just makes sense to think that plasticity must have opportunity to develop. Thank you.